Method of prestressing tension bars of a lock gate



Nov. 7, 1961 o. E. DEAN ETAL 3,007,233

METHOD OF PRESTRESSING TENSION BARS OF A LOCK GATE Filed April 24. 1959 INVENTORS. 14 l0 Orville E. Dean John L. Layshock Stephen 6. Shock BY \MMML 6M4 THEIR ATTORNEYS ttes This invention relates to locks which raise and lower watercraft from one level to another on rivers and lakes particularly to a method of prestressing tension bars mounted upon gates or leaves of the locks or dams. Our invention is especially directed to prestressing the tension bars in order to support the lock gates and make them plumb.

For dam and lock gates to operate properly, they must be plumb so that each closes and opens easily when handling water traihc. Making a lock or dam gate plumb is a difficult and sizeable undertaking since each of the gates may weigh up to 250 tons or more.

In the accompanying drawings, we have shown two leaves of a lock gate on which we practice our method, in which:

FIGURE 1 is a downstream side elevation view of one type of leaf with diagonal tension bars having electric induction heating coils wound on a part of their length; and

FIGURE 2 is a downstream side elevation view of a second type of leaf showing diagonal tension bars mounted thereon.

FIGURE 1 shows a leaf 1 of a lock gate with a miter side 2 and a quoin side 3. Extending from the top of the quoin side 3 diagonally to the bottom of the miter side 2 are three tension bars 4, 5 and 6, sometimes called working diagonals, and extending from the top miter side 2 to the bottom quoin side 3 are two tension bars 7 and 8, sometimes called balancing diagonals. Each tension bar has a turnbuckle 9 for taking up slack therein. To operate the turnbuckles, a device such as a come-long, a chain fall on a wrench with a 3 or 4 foot handle, or other similar device, is employed. As shown, each end of each tension bar is anchored to the leaf.

The leaf 1 of FIGURE 1 is representative of an allwelded construction which weighs up to 250 tons or more.

FIGURE 2 shows a second type of lock gate 10 having a quoin side 11 and a miter side 12 and having a tension bar 13 which extends diagonally downward from the top quoin side to the middle of the bottom side 14 of the gate. This tension bar is also sometimes called the working diagonal. Extending from the middle of the top side 15 of the gate 10 to the bottom of the miter side 12 is a second tension bar 16. Also extending from the center of the top of the gate diagonally downward to the bottom quoin side is a tension bar 17 and extending diagonally downward fro-m the top of the miter side 12 to the middle of the bottom side of the gate is a tension bar 18. Each of the four tension bars 13, l6, l7 and I8 has each of its ends anchored to the gate 1 and each bar has a turnbuckle '19.

As shown in the drawings, the gates have diagonal tension bars which are prestressed to plumb the gate or leaf. The bars are usually disposed so that some extend diagonally from the top quoin side of the leaf to the bottom miter side and other diagonals extend from the top miter side of the gate to the bottom quoin side (FIG- URE 1). Each of the tension bars has a turnbuckle 9, 19 or other similar device for prcstressing them by taking up slack therein and by subjecting them to tension.

Unite A major problem experienced in installation and adjustment of lock gates has been prestressing the tension bars to make plumb the gate. Heretofore, prestressing to plumb the gate at the time of installation and thereafter for adjustment to place the gate back into plumb after it has sagged and gotten out of plumb during usage has required mechanically overstressing a part of the gate by hydraulic jacks disposed at diiferent points on the gate. When using the hydraulic jacks, the top and bottom quoin corners are, of course, held against movement out of the vertical plane of the gate by the hinge on which the gate swings. The bottom miter corner of the gate is fixed by some means to prevent its movement out of the vertical plane of the gate and the top miter corner is then forced out of the vertical plane of the gate by the jacks to produce slack in the tension bars and thus permit taking up the slack to prestress the tension bars. The hydraulic jacks are disposed at the top miter corner of the gate of FIGURE 1 and operated so that they first urge the top miter corner out of the vertical plane of the gate and in a direction upstream viewing FIGURE 1 which is a downstream elevation View, thereby imparting slack to diagonals 4, 5 and 6. When these diagonals thus are placed in a slack condition, their turnbuckles 9 are operated to take up the slack generated by operation of the jacks so that when the force is removed, the top miter corner returns to its original position and simultaneously places the three diagonals under tension. Next, the top miter corner is forced by the jacks in the opposite direction out of the vertical plane of the gate, namely, downstream, whereby slack occurs in diagonals 7 and 8. Then the slack in the two diagonals is taken up through operation of the turnbuckles and the force imparted to the top miter side is withdrawn so that all of the diagonals are prestressed.

When bending the top miter side to impart slack in the two diagonals, there is a likelihood of snapping or substantially overstressing the already pr-estressed three diagonals 4, 5 and 6. Furthermore, when bending the top miter corner in either direction for the purpose of imparting slack to either diagonals 7 and 8 or to the three diagonals, each of these diagonals is subjected to forces which tend to bow them in a longitudinal direction and thereby impose a binding force upon the threads of the turnbuckle. This binding force makes operation of the turnbuckle difficult and even impossible, and sometimes results in stripping the threads.

In addition to the foregoing, there are problems experienced in use of hydraulic jacks due to the torsional stress imparted in the entire gate when bending the top miter corner out of the vertical plane of the gate.

The use of these jacks to pres-tress the tension bars is slow, difficult and costly and must be done in the dry which requires pumping out the locks and closing them down for a period of about thirty days. One substantial undertaking in using the jacks is preparation necessary for pumping out the locks and fixing the lower miter corner against movement out of the'verticatl plane of the gate. Our method of prest-ressing the tension bars which are mounted upon a dam gate or leaf is far less difiicult and costly and avoids the many problems experienwd in using the jacks including shutting down the locks for thirty days and fixing the bottom miter corner against movement. In addition, our method does not require racking the top miter corner in order to produce slack in the tension bars so that the turnbuckles may be operated to impart a residual tension in the bars upon removal of the force at the top miter corner. Specifically, our method comprises the steps of taking up slack in the tension bar or bars mounted upon a look gate on each bar by operation of a turnbuckle or other similar means.

Then, we heat a part of the length of the bar by subjecting the part to electrical induction power for bringing about longitudinal expansion of the part of the bar. During the heating of the part of the bar, We take up the slack resulting therefrom as the heating progresses and produces the longitudinal expansion. When the bar has expanded a predetermined amount and the slack resulting therefrom has been taken up, We terminate heating and then allow the bar to cool to ambient temperature, thus imparting a residual tension thereto.

As shown in FIGURE 1, there is a plurality of coil turns 20 on each of the three diagonal tension bars 4, 5 and 6. These turns are connected in series with lead wires 21 and 22 joined to a source of 400 cycle power (not shown). Wrapped around the part of the length of each of the bars under the coil turns is asbestos paper 23. The purpose of the asbestos paper is to retain the heat in the bars and retard its dissipation into surrounding structure of the leaf or the atmosphere.

One way of carrying out our method includes supporting the leaf so that it is level and plumb before commencement of the prestressing operation. However, this supporting of the leaf is not essential but sometimes is required by specifications for installation or adjustment of a lock gate or leaf.

Prior to heating the tension bars, we tighten the turnbuckles of each diagonal as much as possible, generally by manual operation thereof, to take up all the slack therein. This is important because it provides "a starting point from which to measure the amount of expansion required to effect a desired amount of residual tension in the bar and to mark on the turnbuckle the point to which the turnbuckle nut is to be turned during heating.

Taking up slack when practicing our invention comprises operating tumbuckles such as the turnbuckle 9 of FIGURE 1 and 19 of FIGURE 2 or other similar devices to remove looseness in the tension bar and longitudinal sag or bowing therein. The turnbuckle nut is rotated to shorten the tension bar and until additional rotation becomes difficult. Preferably this amount of operation of the turnbuckle places a small amount of stress in the bar.

Where a tension bar sags because of its length and/or weight, it should be supported to remove the sag resulting therefrom and to avoid binding of the threads of the turnbuckle. This support can be removed once the bar has been prestressed.

The amount of longitudinal elongation or expansion required to bring about -a desired residual tension is determined and then translated into turns of the turnbuckle nut. We select a Zero point on the turnbuckle nut and on its adjacent bar threads after taking up slack in the bar prior to application of heat thereto. Then this Zero point is marked on the nut and on the threads preferably by a chisel or prick punch. Next the determined linear distance or expansion desired is measured along the threads to fix a stopping point for turning the turnbuckle nut. This stopping point is likewise marked by a chisel or prick punch on the threads of the turnbuckle.

With knowledge of the specified residual tension, we determine the amount of elongation or expansion required to produce the tension. Determination of the amount of expansion necessitates taking into consideration length, cross section and composition of the bar, pitch of the threads of the turnbuckle and diameter thereof. In addition, factors such as design and dimension of the leaf, location of the tension bars, workmanship in the shop and at the dam site are taken into account for they affect ability of the leaf to resist tension pull of the tension bars. Despite taking into account all the foregoing factors, we have found from experience that to produce a specified residual stress in a tension bar, calculations employed to determine how much heating and how much expansion is required must be increased by a multiplying factor. In the work which we have done for gates 60 feet high and 61 /2 feet wide with diagonals 8" x 1 /2" x 66 feet and in gates 30 to 40 feet high and 61 /2 feet wide with diagonals 6 to 8 x 1 /2" x 34 feet and diagonals 6 to 9" x 1 /2 to 1% x 42 feet long, the multiplying factors have ranged from about 1.5 to 1.9. One reason for these multiplying factors is, we believe, a settling which takes place in the gate when the tension bars are prestressed.

In practicing our method on a gate of the type shown in FIGURE 1 where the gate was 60 feet high and 61 /2 feet wide and each diagonal 8 x 1%" x 66 feet, calculations showed /2" expansion in the entire 66 foot length was required to bring about a stress of 18,000 p.s.i. and a expansion in the entire 66 foot length for a stress of 23,000 psi. The turnbuckles on these diagonals had 2% threads per inch and a diameter of 4%. Therefore, to effect a stress of 18,000 p.s.i., .656 turn of the turnbuckle nut according to calculations is required. This .656 turn of the nut is equal to a circumferential travel thereof of about 9.8. According to our calculations, to produce a stress of 23,000 p.s.i., the amount of circumferential travel of the nut is about 12.5. Further calculations showed that to expand the 66 foot bar /2, a temperature of 775 F. was necessary.

However, when prestressing the 66 foot bars which correspond to bars 4, 5 and 6 of FIGURE 1, to produce a stress of 18,000 p.s.i., we heated about 25 feet of the length of each bar for about 3 hours 50 minutes to a maximum temperature of about 550 F. using 48 coil turns and 400 cycle, 1.80 volt, ampere power source. In this operation, we found that a circumferential travel of 9.8" did not produce 18,000 p.s.i. stress but that a 15% circumferential travel was required to effect a stress of 18,000 p.s.i. By using a multiplying factor of 1.6 and the 9.8 circumferential travel, we obtained the value of 15%circumferential travel which is equal to about .800" expansion of the 66 foot length.

To effect a stress of 23,000 p.s.i. in tension bars corresponding to bars 7 and 8 of FIGURE 1, we heated 25 eet of the length of each bar for about three hours to a maximum temperature of 600 F. using 65 coil turns connected to a 400 cycle, 180 volt, ampere power source. Instead of 12 /2" circumferential travel of the turnbuckle nut as indicated by the calculations, our experience indicated use of a multiplying factor of 1.5 or 18% circumferential travel. The 18%" circumferential travel produced 23,000 p.s.i. in the tension bar which amount of travel is equal to about .960" expansion in the 66 foot length.

Because we heat only a part of the length of the bar, it is necessary to increase the temperature from that indicated by the calculations so that the part of the length heated expands sufficiently to ensure the specified residual stress when slack produced by the heating has been taken up and the bar allowed to cool to ambient temperature. The rate of heating which we employ is such that expansion caused by the induction power is taken up substantially as it occurs by operation of the turnbuckles. The rate of heating should not be so fast that expansion produces longitudinal buckling or bowing of the tension bars and thereby causes binding of the threads of the turnbuckle.

Preferably, a thin insulating material such as the ashestos paper 23 or glass tape, or other similar material, is wound about or wrapped around that part of the length of the bar which is subjected to induction heating. The purpose of this insulation material is to retain the heat in the bar and retard loss thereof to the surrounding structure or the atmosphere. However, it is not necessary that the heat insulating material be employed.

To heat a bar, insulated, flexible, current carrying cable is wrapped around the length of the bar to form the coil turns 20 of FIGURE 1. For a tension bar 42 feet long, We have heated about 18 feet of its length to produce residual stresses of about 8,000l9,000 psi. and for a tension bar 66 feet long, we have heated about 25 feet of its length to produce residual stresses of about 15,000- 29,000 p.s.i. The adjacent coil turns are from 1 to inches apart depending upon the amount of heat desired and preferably, spacing between turns is about 3 to 4 inches. The amount of spacing between the coil turns is subject to adjustment to take into account composition of the metal, length of the part of the bar to be heated, required amount of expansion, number of bars being heated simultaneously, and capacity of the source of electric power.

We have found that a 400 cycle power source is preferable and that power sources of lower cycles such as 250 and higher cycles can be used provided that the cycle employed does not generate excessive heat in the coil turns. Generally, it is impractical to employ coil turns which have cooling provisions therefor such as a tube through which Water runs. The current carrying conductors which form the coil turns should be flexible so that they can be easily wound around the tension bars and removed therefrom and, of course, if there is a tube for conducting water therethrough which tube is in engagement with the current carrying conductors, flexibility of the conductors is materially decreased.

To measure residual tension in the bars, we employ electric strain gauges which accurately measure the tension. However, a number of other tension measuring devices can be used. The electric strain gauges which are sometimes called patches comprise a plurality of wires which carry an electric current and which are bonded onto a part of the tension bar. These strain gauges are well known and further description thereof is deemed unnecessary. Preferably, we locate the strain gauges away from that part of the bar subjected to heating.

Before beginning prestressing and after slack has been taken up in the tension bar, we take a reading from the strain gauges and then after the bar has been heated, after slack has been taken up from expansion resulting from the heating, and after the bar has been allowed to cool to ambient temperature, a second reading is made. The differences between the two readings is used in well known formulas to ascertain the amount of residual tension in the bars.

During heating of the bars by use of induction power, the turnbuckle is continually operated to take up the slack caused by expansion due to the heating. It is desirable to substantially continually take up this slack so that binding of the threads of the turnbuckle is avoided as the result of expansion of the bar. Heating of the bars on the gate with each end of each bar anchored to the gate is carried on until they have expanded a predetermined amount and the turnbuckles have been operated to take up the slack resulting from the heating and expansion. Operation of the turnbuckles comprises rotation of the turnbuckle not from its starting point to the indicated stopping point on the threads. Heating of the bars may also be practiced until the bars have expanded a sufficient amount to permit the turnbuckle nut to be rotated from the starting point to the indicated stopping point on the threads. Then heating is terminated and the bar allowed to cool to ambient temperature. If after cooling the residual tension is too high, We reheat a part of the length of the bar and back off on the turnbuckle until after cooling the desired amount of residual tension is in the bar. On the other hand, if the residual tension is too low, there is a reheating to produce further expansion and a taking up of additional slack resulting therefrom to increase the residual tension.

The temperature at which We carry out our method varies from a few degrees above ambient temperature to a few degrees below melting point of the metal. Preferably, the temperature for steel ranges between about 150 F. and 750 F. Care should be taken to avoid excessive temperatures which may destroy or adversely affect heat treatment of the metal or which will excessively weaken or soften the metal. Also we avoid approaching temperatures whereat a change in the crystal structure of the metal occurs such as the lower critical temperature in steel at about 1670 P. where alpha body centered iron changes to gamma face centered iron.

Electrical induction heating enables us to efficiently,

and effectively heat the tension bars to bring about the necessary amount of expansion for prestressing. Electric induction power heating uniformly heats a bar from its periphery to its core and the heating is fast and subject to good control. Use of a flame impinging upon the bar is clearly undesirable because of inability to heat uniformly, inability to control heat and danger of damaging the metal, of destroying heat treatment in the metal, and of burning the metal. Considering the fact that prestressing of the bars must be carried out on the gate with both ends of each bar anchored to the gate, electric induction heating is well suited for our method of prestressing. Other ways of heating the bars such as with some sort of a fuel-fired small furnace would be most awkward and impractical.

Our method of prestressing the tension bars has significant advantages over those methods heretofore employed. In the first place we can prestress the tension bars of a leaf in about one or two days without having to pump out the lock and to secure the lower miter corner from movement. The mechanical method of prestressing using jacks requires thirty days and pumping out the lock together with securing the lower miter corner of the gate from movement.

In the second place, our method does not tend to effect a binding of the threads of the turnbuckle because the electric induction heating of the bars is such that the turnbuckles are operated as expansion occurs and bowing of the bars with resultant binding is avoided. In the case of the mechanical method with the jacks, binding of threads of the turnbuckle frequently occurs for it is extremely diflicult to operate the jacks to avoid longitudinal bowing of the bars with consequent binding of the threads. This is because operation of the jacks frequently produces amount of slack which cannot be taken up fast enough to avoid the bowing.

In the third place, practice of our method is free from danger of overstressing or breaking tension bars which have already been prestressed when prestressing unstressed bars. In the mechanical method using jacks, there is a danger of breaking already prestressed bars when subjecting the top miter corner to force so that unstressed bars can be prestressed.

In the fourth place, our method does not subject the leaf or gate structure to distortion as does the mechanical method when the jacks bend the top miter corner upstream or downstream.

While certain preferred embodiments of our invention have been shown and described, it will be understood that it may be otherwise embodied within the scope of the appended claims.

We claim:

1. A method of positioning a lock gate for a waterway upon its mounting for opening and closing said gate by imparting a predetermined amount of residual tension to tension bars mounted upon the lock gate with each end of the bars anchored in place on the gate, each bar having a means for taking up slack therein, comprising the steps taking up slack in said bars, then heating a part of the length of the bars by subjecting the part to electrical induction power to produce longitudinal expansion in said bars, during heating of said bars, taking up slack therein which results from longitudinal expansion due to the heating, terminating the heating of the bars when they have expanded longitudinally a predetermined amount and allowing the bars to cool to ambient temperatures to impart a residual tension therein, said heating being carried out so as to produce an amount of longitudinal aoozass expansion greater than that determined by calculation to impart said predetermined amount of residual tension in said bars.

2. The method of claim 1 characterized by said heating being carried out at a rate which permits substantially continuously taking up of slack in said bar.

3. The method of claim 1 characterized by marking on said bar a point to Which said taking up slack means is to be operated to obtain said predetermined amount of residual tension in said bar and terminating the heating of the bar and operation of said taking up slack means when said taking up slack means has reached Said point.

4. The method of claim 1 characterized by prior to the step of taking up slack in said bars, supporting the gate in a given position whereat said gate can pivot on its mounting to open and close.

5. The method of claim 1 characterized by in said heating raising the temperature of said bar into a range from about 150 F. to about 750 F.

6. The method of claim 5 characterized by prior to the step of taking up slack in said bars, supporting the gate in a given position whereat said gate can pivot on its mounting to open and close.

7. The method of claim 1 characterized by in said heating raising the temperature of said bar into a range from about 150 F. to about 750 F. and carrying out said heating at a rate which permits substantially continuously taking up slack in said bar.

8. The method of claim 7 characterized by prior to the step of taking up slack in said bars, supporting the gate in a given position whereat said gate can pivot on its mounting to open and close.

Cir

9. The method of claim 1 characterized by so heating said bar as to produce the amount of longitudinal expansion from about 1.5 to about 1.9 times greater than that determined by calculation to impart said predetermined amount of residual tension.

10. The method of claim 9 characterized by said heating being carried out at a rate which permits substantially continuously taking up of slack in said bar and by in said heating, raising the temperature of said bar into a range from about F. to about 750 F.

11. The method of claim 9 characterized by said heating being carried out at a rate which permits substantially continuously taking up of slack in said bar, by in said heating raising the temperature of said bar into a range from about 150 F. to about 750 F., and by prior t0 the step of taking up slack in said bars, supporting the gate in a given position whereat said gate can pivot about its mountings to open and close.

12. The method of claim 9 characterized -by in said heating raising the temperature of said bar into a range from about 150 F. to about 750 F.

13. The method of claim 12 characterized by prior to the step of taking up slack in said bars, supporting the gate in a given position whereat said gate can pivot on its mounting to open and close.

References Cited in the file of this patent UNITED STATES PATENTS 1,980,875 Northrup Nov. 13, 1934 1,981,630 Northrup Nov. 20, 1934 1,995,313 Leake Mar. 26, 1935 2,040,721 Zimmerman May 12, 1936 2,184,534 Smith Dec. 26, 1939 

